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What is the purple wire on the ignition switch?

The ignition switch is a critical component in your vehicle’s starting and electrical system. It activates when you insert the key and turn it to the “On” position, sending power to the engine control unit, fuel pump, and other electronics necessary to start the engine. The ignition switch also contains electrical contacts for accessories like the radio, windshield wipers, and lights.

Wiring Colors and Functions

The wires coming out of the ignition switch are color-coded to identify their purpose. Though colors can vary between vehicle makes and models, some common ignition switch wire colors are:

  • Red – Power from the battery when key is in the “On” position
  • Yellow – Power from battery when key is in “Start” position
  • Brown – Accessory power for radio, wipers, lights, etc.
  • Blue – Power for dash lights and engine diagnostic system
  • Black – Ground wire
  • Green – Ignition relay control wire
  • Purple – Starter motor control wire

So in most cases, the purple wire coming from the ignition switch will connect to the starter solenoid or relay. When you turn the key to the “Start” position, it sends power through the purple wire to engage the starter motor and crank the engine.

Common Ignition Switch Configurations

There are a few common ignition switch configurations, which will determine exactly how the purple starter wire is utilized:

Standard Ignition Switch

A standard ignition switch has distinct “Off”, “On”, and “Start” positions. In this configuration, the purple wire only receives power when turning the key to “Start”. It activates the starter solenoid which then cranks the starter motor.

Momentary Ignition Switch

Some vehicles have a momentary ignition switch where you push the key in to “Start” and it returns to “On” when released. On these, the purple wire may connect to a start button elsewhere on the dash that you press while the key is in the “On” position.

Push Button Start

On newer vehicles with push button start, there is no physical ignition switch. Turning on the car powers up the ignition system, while pushing the Engine Start/Stop button sends voltage through the purple wire to engage the starter. There may also be a backup method to start the car if the key fob battery dies.

Additional Ignition Switch Wire Functions

Let’s look at some other important functions that may be controlled through wires coming from the ignition switch:

Red Wire

The red wire provides power to the vehicle’s electrical system when the key is turned to “On” or “Start”. This energizes all the electronics like the engine control module, fuel pump, oxygen sensors, etc. needed to start and run the engine.

Yellow Wire

On GM vehicles, the yellow wire is only hot in the “Start” position to engage the starter motor. It activates the solenoid to crank the engine without engaging the ignition system.

Brown Wire

The brown wire usually powers accessories like the radio, windshield wipers, power windows, etc. This allows these systems to operate even when the key isn’t in the “On” position.

Blue Wire

The blue wire typically connects to the gauge cluster, warning lights, and engine computer diagnostic systems. This allows diagnosing problems prior to starting the engine.

Green Wire

The green wire activates the ignition relay, sending power to the ignition system when turning the key to “Start”. This engages the spark plugs and fuel injectors/carburetor to fire up the engine.

Locating and Testing the Purple Starter Wire

If you need to find the purple starter wire to test or replace it, here are some tips:

  • Consult a vehicle wiring diagram to trace the wire from the ignition switch to the starter solenoid/relay.
  • The wire may run directly to the starter or to an intermediary relay/solenoid switch first.
  • Check for voltage with a multimeter when the key is turned to “Start” to identify the purple wire.
  • Perform a voltage drop test to check for excessive resistance indicating a faulty wire.
  • Test wire continuity to isolate breaks or damaged sections.

Being able to locate and test the purple starter wire is important when troubleshooting ignition switch or starter issues. Tracking down problems with this wire can save significant repair time and get your engine cranking properly again.

Common Purple Wire Problems

Here are some typical issues that can occur with the purple starter wire and ignition switch:

Loose or Damaged Connections

Vibration, corrosion, and wear can cause the purple wire connections to become loose or damaged. This leads to intermittent or no starter engagement when trying to start the engine. Check the condition of all wire connections and terminal ends.

Faulty Ignition Switch

If an internal failure occurs within the ignition switch, it may not send voltage through the purple wire in the “Start” position. This will cause a no crank condition. Test the switch with a multimeter and replace if necessary.

Broken/Damaged Wire

The purple starter wire can become damaged from heat, chafing, or corrosion. This can create an open circuit so the starter doesn’t activate when trying to start the car. Inspect the entire length of the wire and repair or replace any damaged sections.

Short Circuits

Exposed sections of the purple wire could short to ground or other wires, diverting power away from the starter motor. This will lead to intermittent cranking issues. Inspect for bare wires contacting metal chassis components or other exposed terminals.

Faulty Solenoid/Relay

While not the purple wire itself, starter relay or solenoid issues can prevent voltage from reaching the starter motor. If the purple wire checks out ok, test the starter solenoid activation circuit for faults.

Diagnosing and Replacing a Bad Purple Starter Wire

Use the following general process to diagnose and replace a faulty purple starter wire if the engine won’t crank properly:

  1. Turn the key to “Start” and listen for the starter engaging.
  2. If nothing happens, check for battery voltage on the red wire at the ignition switch.
  3. If no voltage on the red wire, test the battery, fuses, and connections.
  4. If red wire has power, test for voltage on purple wire at switch.
  5. No voltage indicates faulty switch or wire. Test switch and inspect wire.
  6. Check for voltage drop across purple wire during cranking. More than 0.5V drop indicates resistance.
  7. Disconnect wire at starter and test for continuity to isolate breaks.
  8. Remove and replace any damaged sections of wire.
  9. Reconnect and make sure starter engages when key is turned.

This basic troubleshooting procedure will help zero in on any issues with the purple starter motor wire and get your engine cranking properly again.

Safety Precautions

When testing and replacing ignition switch wiring like the purple starter wire, keep in mind these safety guidelines:

  • Disable ignition system by disconnecting battery before doing any work.
  • Follow wiring diagrams closely and make sure all connections are proper.
  • Use care when probing wires and piercing insulation.
  • Protect exposed wire ends and connections from shorting.
  • Handle ignition switch carefully and don’t force key/lock cylinder.
  • Reconnect battery only after all wiring is intact.
  • Tester for proper function before starting engine.

Working with ignition components can be hazardous if proper precautions are not taken. Following safety procedures will prevent electrical shorts, shocks, and other injuries or fires.


The purple wire coming from the ignition switch serves the critical function of activating the starter motor to crank over the engine on signal. While not the only wire involved in the ignition process, diagnosing and resolving problems with the purple starter wire is key to getting your engine turning over properly. Locating and testing this wire, resolving loose connections, damage, or shorts, and replacing faulty sections can get your vehicle started and back on the road.